Atma-Sphere MA-1 amps

I swap tubes around every few months - there are many great combinations. NOS tend to last much longer than contemporary brands - or so everyone says - I haven't had a 6SN7 go south on me yet, so no direct experience.

MA-1 Mk.III ---
Driver: Sylvania GTA or RCA GTB
Tubes 2&3: VT-231 Ken-Rads (these positions have biggest influence on sonics, imo), RCA Grey Glass
Tubes 1&4: VT-231 Sylvania, RCA Grey Glass, or VT-231 Raytheon

I really like the VT231 Ken-Rads in the the amps. They're still out there but getting a bit (more) pricey.

Couple notes:
i) My Mark IIIs are in the traditional narrow chassis, so position may be different w/ the newer style. Driver is understood as position #5 at the edge of the chassis facing the output tubes.
ii) For NOS, the driver position requires a GTA or GTB - something that supports a higher 450VDC plate voltage; the other positions do just fine with other NOS (eg. GT or VT231).

The preamp is both challenging and fun because of the phono section, where it is harder to get good *quiet* tubes - but its definitely doable.

MP-1 ---
forwardmost 6SN7: VT-231 Ken-Rad
other 6SN7: Electro-Harmonix or stock Chinese
phono (12AT7s): CV4024 Mullards, '60's Siemens 12AT7s, 6201 Sylvania Gold Brand

I put Herbies Tube Dampers on 3 of the 5 6SN7 per channel and 3 of 4 12AT7s per channel. The dampers work well.

check this out:
The Reference 6SN7 Thread

The gear is incredibly revealing of tube changes (for that matter any change) and tube rolling becomes lotsa fun. Good section matching w/in a tube is v. important.
 
Tim
 

Just in case anyone is unfamiliar with it, there is also a version of the MA1s that come with 4 12SX7 tubes in lieu of the 6SN7s. This is the version I own. Rolling 12SX7s isn't an issue, as there are not many to choose from. Cheers,

Spencer

Spencer, we've not used 12SX7s at any time, but at one time it was a popular field modification. The 12SX7 has similar specs to the 6SN7 and it is easy to set op the filaments for 12V, so it was a way to get access to an unused tube stock.

Ralph, is there any problem using US made (e.g., GE) NOS 6AS7s with MKIII amps? I thought I read somewhere that they could be a problem with fixed bias amps (I take it the MKIIIs are not).

Please let's not forget that the Chinese-manufactured 6SN7s are actually very nice tubes. I've paid a bit of a premium for Sophia tester "A matched" metal base military pieces from DIY HiFi Supply, but still only $18 apiece.

Matched pairs of Baldwin labeled 1965 vintage Raytheon GTB are being sold by Brent Jessee, a reliable vendor, for $45/pair.

I just took a gamble on four supposedly "matched" quads of Baldwin labeled Sylvanias of late 50s/early 60s vintage with the BIG chrome domes from Ebay at under $15/tube. The photos are quite sharp and show very clean tubes with spotless pins. We'll see how they test on my B&K Model 700...

One needn't pay upwards of $100/pair or even much, much more for quality 6SN7s. Just doesn't make sense.